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that Dr. A. Dohrn has described and figured under Cuma a rather complicated 
system of arterial vessels issuing on each side from a single stem originating 
from the heart. Through this system, the blood is said to be carried both 
backwards and forwards, the vessels, especially in the walls of the carapace, 
exhibiting abundant ramifications. There can be no doubt that this statement is 
based upon direct observation; but I suspect that the existence of these vessels 
has merely been assumed from the course of the blood-corpuscles, which indeed 
circulate through the body with great regularity, though not in my opinion, 
enclosed in any distinctly defined vessels. 
3. Renal System. 
Under this head, I may mention a pair of problematic organs occurring 
in all Cumacea, one on each side of the heart, and easily observable owing to 
their opaque whitish colour (see PI. LXV—LXVIII. fig. 1, n). These organs 
have the form of rather short, somewhat curved tubes, exhibiting several rounded 
lobules and slightly diminishing in thickness behind (see PL LXVI, fig. 6). They 
contain a uniform, finely granular mass without any cellular elements (see fig. 7), 
the granules, under a high magnifying power, exhibiting a somewhat irregularly 
angular form, and thus resembling calcareous concretions. I have failed to detect 
any excretory duct, and indeed, I am of opinion that strictly speaking these 
organs are not secretory, but that they merely serve as storing places for some 
unserviceable matter secreted from the blood. I long ago 1 ) described a pair 
of undoubtedly homologous organs in Asellus aquations, where they likewise occur 
on each side of the heart, and at that occasion I expressed a similar opinion 
as to the significance of these organs. 
4. Nervous System. 
As in other Crustacea, the central parts of the nervous system consist 
(see PI. LXVI, fig. 2) of the cephalic ganglion situated in front dorsally, and 
the fiervous chord running along the ventral side of the body. The latter is 
composed of a series of 16 ganglia connected by double commissures. Of these 
ganglia the first 10 belong to the anterior division of the body, and are much 
larger than the remaining 6 caudal ones, which, with the exception of the last, 
are very slight, almost obsolete. All the ganglia consist of 2 symmetrical parts, 
0 Crustaces d’eau douce de Norvege. 
